Flexible displays, e-paper are around the corner

Portland, Ore.  Next year might be dubbed the year of the flexible, as roll-up displays and digital signage made of electronic paper debut. Ultrathin displays and e-paper took center stage at the Americas Display Engineering and Applications Conference here last week, with researchers reporting progress and predicting a 2006 deployment. Conference goers also heard of advances in LCD technology and in military-grade head-mounted displays.

Nick Colaneri, associate director of the Flexible Display Center at Arizona State University in Tempe, outlined progress at that Army-funded center for the process development and pilot production of flexible backplanes and displays. "We started at zero a year ago, but now we have a large database from our transistor tests so far. We have an enormous amount of data to use in optimizing our process," he said.

The target technology is organic pentacene transistors that can be fabricated at a cool 90°C, as well as other low-temperature formulations, for which the team uses in-house electrophoretic front-plane lamination. The Tempe center's 19 engineers and technicians have run 38 lots through the thin-film transistor (TFT) pilot line, probed 385 test wafers and built an automated database with 11,521 transistors.

Colaneri said that in just one year the transistors went from very low performance to within 20 percent of normal. "At first we weren't worried about how high performance our transistors were  we had other problems to solve," he said. "But now that we have concentrated on increasing transistor performance, we have electron mobility up to 0.1 cm2 per volt, which compares to a norm of about 0.5 cm2/V."

The center will begin qualifying its second-generation TFT pilot line in 2006 and start prototyping with it in 2007. The second-generation line will forgo round wafers for a 14.5 x 18.5-inch rectangular-plate form factor, which creates a 23-inch-diagonal display that the researchers plan to dice into four 10-inch displays.

Flexible Display Center member companies are also providing facilities for research on electrophoretic ink for paperlike displays at E-Ink Corp. (Cambridge, Mass.), and on cholesteric liquid crystals for reflective and near-infrared displays at Kent Displays Inc. (Kent, Ohio). Unlike electrophoretic ink, which is monochromatic, cholesteric liquid crystals create full-color reflective displays without filters.

Meanwhile, Amy Chen, business development manager at SiPix Imaging Inc. (Fremont, Calif.), described progress toward commercial production of the company's full-color e-paper. SiPix's Microcup Electronic Paper is flexible, high-contrast and offers nearly a 180° field-of-view, but also is ultralow in power. Because it needs power only to change a pixel's color, it has zero standby power.

"We have the world's first roll-to-roll for EPD [electrophoretic displays]," said Chen. "Currently we are running at 6 inches per minute."

Microcups are built on a 150-micron flexible plastic substrate. It includes a transparent conductor that uses indium tin oxide to form domains 80 to 150 microns square, into which colored dyes can be deposited. The Microcups are then hermetically sealed and laminated onto an electrode-studded backplane that drives the display. Manufacturing uses a roll-to-roll embossing process whereby a continuous sheet of PET plastic is coated, first, with transparent conductors and then with a proprietary resin. The microembosser then molds the Microcups into the resin so they can be filled with dyes, hermetically sealed and attached to the backplane.

"We are currently working on applications with BASF, Philips and others," said Chen. "Starting in 2006, you will begin to see our Microcup EPD used for signage application, such as for shelf price stickers, for roll-up displays and on smart cards."

Last month, Philips Polymer Vision said it was on track to deliver in 2006 a 1:10 contrast ratio, 100-micron-thick, 5-inch, 320 x 240-pixel roll-up display it developed with E-Ink's monochrome electronic ink. According to Chen, Philips is also doing cooperative development with SiPix toward a color version of the roll-up displays. E-Ink, for its part, recently announced a 12-bit technology that uses filters to achieve color with its E-Ink product.

Military head-mounted displays were described by Primordial (Saint Paul, Minn.). Its Primordial Soldier heads-up vision system applies tactical overlays, including annotations that label friend from foe on a soldier's HMD, perform automatic threat assessment and provide statistics on vulnerabilities. Heads-up displays were once limited to tank operators and fighter pilots, but the Primordial Soldier for infantrymen will be included in the Army's Future Force Warrior early-user evaluation at Fort Benning, Ga.

A revolutionary improvement for LCDs harnessing the human visual system was unveiled by Clairvoyante (Sebastopol, Calif.). Founder and CTO Candice Brown Elliott showed how algorithms that add white stripes to red, blue and green ones can fool the eye into perceiving a screen that is twice as bright for the same power (or the same brightness at half the power). The company's PenTile RGBW subpixel renderings reduce by one-third the number of pixels needed for a given resolution, she said.